SOMERSET TWP, Somerset County — A Butler County man was killed Tuesday morning when he lost control of his tractor-trailer and crashed on the Pennsylvania Turnpike, authorities said.

Robert M. Grazier, 61, of Middlesex Township was pronounced dead at the scene of the accident about 5:15 a.m.

State police said Grazier’s rig was westbound when he traveled off the north side of the highway and onto the grass berm. The truck hit a mile-marker sign, which caused Grazier to “abruptly swerve to the left and apply the brakes,” according to a police report.

The tractor-trailer traveled across both lanes and slammed into a concrete median barrier. The vehicle climbed on top of the barrier, police said, and overturned, landing on its side and ejecting Grazier from the cab.

Police said he was not wearing a seat belt.

Somerset County Coroner Wallace Miller pronounced Grazier dead about 8 a.m. An autopsy was performed later that day, but the cause of death was pending toxicology and other tests, which could take several weeks.

Wallace said drugs and alcohol were not suspected.

Police did not immediately know what caused the crash, which remains under investigation.